This study demonstrated that the wavelength, exposure time and intensity of daylight contribute to change and improve the brain’s working speed, reaction time, emotional responses and general functions, such as judgement and acumen. Particularly the blue part of light had an effect on human behaviour.

See the study here her

Light as a modulator of cognitive brain function

Vandewalle G, Maquet P, Dijk DJ.

Trends in Cognitive Science, 2009 Oct;13(10):429-38.